Parkinson's disease (PD) is a debilitating neurodegenerative disease that affects over i million individuals in the US. Dementia with Lewy Bodies (DLB) is second in occurrence only to Alzheimer's disease. There are presently no treatments for PD or DLB that can halt or reverse the neurodegenerative processes. The RNA interference (RNAi) gene therapy approach in this project has the potential of halting or reversing these diseases. Recent studies suggest a role for a-synuclein (SNCA) in the development of PD and DLB, and other neurodegenerative diseases classified as a-synucleinopathies. Three point mutations in the SNCA gene, as well as triplet SNCA gene repeats, have been linked to familial forms of PD and DLB, revealing both mutant and wild type SNCA as therapeutic targets for these diseases. SNCA is a main components in neuronal inclusions called Lewy bodies, the neuropathological hallmarks of individuals afflicted with PD or DLB. In PD, Lewy bodies are found predominantly in the substantia nigra where the degenerating dopaminergic (DA) neurons reside. In DLB, Lewy bodies are found in many cortical and subcortical structures. Lewy neurites, neuronal processes containing insoluble SNCA protein, are found in both diseases. Insults that lead to death of DA neurons in animal models of PD, including exposure to the pesticide, rotenone, the neurotoxin, MPTP, and drugs that inhibit protein degradation increase SNCA expression and result in SNCA containing Lewy body-like inclusions in DA neurons. Moreover, experimentally increasing expression of human SNCA in a range of laboratory species leads to DA neuronal pathology and functional deterioration. We propose to explore the hypothesis that inhibiting expression of SNCA in DA neurons using a gene therapy approach will prevent DA neurodegeneration. Adeno-associated virus (AAV), the vector of choice for clinical trials will be used in rats in which human SNCA is ectopically expressed in DA neurons leading to DA cell death. The effects of silencing SNCA expression in this model, as well as in an SNCA-dependent cell culture model, will be assessed using morphometry, histology, neurochemistry and behavioral testing. Also, a vector with the silencing construct under control of an inducible promoter will be generated and tested as a possible safety strategy for a clinical gene therapy. The goal of this project is to generate proof-of-principle data supporting the development of clinical trials using a novel RNAi-based gene therapy for individuals afflicted with PD and DLB. ? [unreadable] [unreadable] [unreadable]